The disclosed subject matter relates to systems and methods for radiative cooling and heating.
Surfaces can absorb and emit heat energy via electromagnetic radiation. The optical properties of a surface can depend in part on the geometry and materials of the surface. During radiative heat transfer, the temperature of a body can increase or decrease depending on the net electromagnetic radiation absorbed by the surface. For example, if the surface absorbs more radiation than is emitted, the temperature of the body can increase. On the other hand, if the surface emits more radiation, the temperature of the body can decrease.
Thermal radiation can be used in passive radiative cooling and heating, i.e., radiative cooling and heating that does not require energy input. Accordingly, passive radiative cooling and heating can be used to reduce the amount of energy required to cool or heat a body. Radiative cooling and heating can be used to reduce the energy cost associated with, for example, commercial and residential buildings, as well as vehicles.
Certain methods of passive radiative cooling use a surface coating that can be applied to buildings with increased reflectivity of incident solar radiation and increased emissivity in a limited spectral range corresponding to the infrared transmission window of the atmosphere. Other techniques can utilize complex multilayer structures that reflect solar radiation and emit thermal radiation for daytime radiative cooling.
However, there remains a need for improved techniques for radiative cooling and heating.